Salinity stress is a major abiotic constraint limiting crop growth and productivity, particularly in arid, semi-arid, and coastal agro-ecosystems. Elevated salt concentrations in the soil adversely affect plant water relations, disrupt ionic and nutrient balance, and trigger oxidative stress, resulting in significant yield reductions. Foliar spray has emerged as an effective supplementary strategy for salinity stress management, as it facilitates direct delivery of nutrients and bioactive compounds through the leaf surface, thereby bypassing the constraints imposed by salt-affected root zones. Current understanding of the effectiveness of foliar spray in alleviating salinity stress is synthesized with emphasis on physiological, biochemical, and molecular mechanisms. The nature and sources of salinity stress and their impacts on plant metabolism are outlined, followed by the principles of foliar nutrition, including pathways of leaf absorption and translocation of applied compounds. The benefits of foliar application under saline conditions—such as rapid nutrient availability, higher use efficiency, and lower dosage requirements—are critically evaluated alongside inherent limitations, including risks of phytotoxicity and environmental factors influencing absorption. Different categories of foliar-applied agents, including mineral nutrients, plant growth regulators, osmoprotectants, antioxidants, signaling molecules, and biostimulants, are discussed in relation to their roles in improving plant water status, maintaining ionic homeostasis, enhancing photosynthetic efficiency, and strengthening antioxidant defense and stress signaling networks. Evidence from crop-specific responses in cereals, legumes, horticultural, forage, and oilseed crops demonstrates the broad applicability of foliar interventions under saline conditions. Future perspectives highlight the need for precision foliar application technologies, nano-enabled delivery systems, molecular and omics-based validation, and long-term field-scale studies to optimize foliar spray strategies for sustainable crop production in salt-affected environments.